Chlamydia trachomotis, an intracellular parasite, is the etiologic agent of trachoma, non-gonococcal urethritis and inclusion conjunctivits. It can also infect the cervix of women and during pregnancy, the organism may be acquired by the infant during passage through the birth canal at delivery. The infant may subsequently develop inclusion conjunctivitis or pneumonia. We intend to investigate in this proposal, the risks and consequences of perinatal chlamydial infection and to explore various means of intervention and treatment. These objectives will be accomplished by means of prospective incidence studies, prophylaxis and treatment trials: 1) We shall study the efficacy of prenatal treatment of pregnant women with chlamydial infection, with erythromycin on the eradication of the infection and the prevention of subsequent chlamydial infection in the infant. 2) Evaluate erythromycin ointment as an alternative neonatal ocular prophylaxis for the prevention of neonatal chlamydial infection. 3) Evaluate oral erythromycin versus topical sulfonamide for the treatment of neonatal chlamydial conjunctivitis. 4) Determine the incidence of pneumonia due to C trachomatis in infants under one year of age and evaluate the comparative efficacy of treatment with oral erythromycin or ampicillin. 5) Determine if C. trachomatis plays a role in middle ear disease in children, and finally 6) Investigate the prevalence of chlamydial infection in the families of infected infants.